416 


Tidal   Evolution 

by 

imgardt 


California 

egional 

icility 


UNIVERSITY  OF  CALIFORNIA 
LOS  ANGELES 


PUBLICATIONS 


ioutbcrn  (California  <5c*encc 


LOS  ANGELES 


CONTENTS: 

Evolution  *  * 

A  Concise  Statement  of  the  effect  of  Tidal  Friction  on  the  Diurnal 
Motion  of  the  Earth. 


B.  R.  BAUMGARDT, 

SECRETHRT  SOUTHERN,  CKLIFORNIH  SCIENCE  ASSOCIHTION. 


LOS  ANGELES: 
PRINTED  FOR  THE  ASSOCIATION. 

1895. 


PUBLICATIONS 


(California  £Jcience 

LOS  ANGELES 


TIDAL  EVOLUTION 


BY  B.  R.  BAUHQARDT. 


All  phenomena  may  be  grouped  into  two  classes — those 
that  are  rythmic  or  periodic  in  their  nature,  and  those  that 
are  constant  and  unchanging,  that  is,  do  not  increase  and  then 
decrease  with  a  regular  rythmic  periodicity. 

To  the  first  class,  which  is  by  far  the  largest,  belong  all 
the  more  obvious  phenomena  connected  with  the  various  man- 
ifestations of  force  in  nature,  such  as  light,  heat,  electricity, 
sound,  motion,  etc.,  as  well  as  those  more  mysterious  ones 
which  we  comprehend  under  the  general  term  of  life. 

The  swaying  motion  of  a  reed  in  a  stream,  the  rustling 
of  the  leaves  in  a  tree,  the  pulsation  of  the  blood  in  the 
arteries  and  veins  of  the  human  body,  the  rise  and  fall  every 
twelve  hours  of  the  tides  on  our  seashores,  the  periodic 
maxima  and  minima  every  eleven  years  of  spots  on  our  pri- 
mary, the  sun,  the  accelerating  and  retarding  motions  of  the 
planets  in  their  celestial  orbits,  the  inequalities  of  our  satellite, 
the  precession  of  the  equinoxes— that  wonderful  wabbling 
motion  of  our  earth's  axis  around  the  celestial  pole  in  a 
majestic  orbit  requiring  25,000  years  for  its  accomplishment — 
the  occillating  change  of  position  of  the  major  axis  of  the 
earth's  elliptical  orbit — the  great  cycle  of  the  solar  system, 
when,  according  to  L,a  Grange,  all  the  planetary  perturbations 
shall  have  compensated  each  other  and  a  new  cycle  commenced, 
the  wonderful  periodic  increase  and  decrease  of  light  in 
many  of  the  variable  stars  and  many  other  astronomical  phe- 
nomena are  all,  I  think,  typical  illustrations  of  the  first  class, 
or  those  that  are  decidedly  rythmic  in  their  nature. 


447065 


6  TIDAL  EVOLUTION. 

But  all  phenomena  are  not  of  this  kind.  There  are  some 
astronomical  phenomena  which,  at  least  in  their  broadest  and 
most  philosophical  sense,  differ  entirely  from  this  class.  They 
do  not  increase  and  then  decrease  in  regular  rythmic  varia- 
bility, and  for  this  reason  differ  entirely  from  the  more  obvious 
ones  such  as  I  have  enumerated.  To  one  of  these  I  am  about 
to  invite  your  attention  for  a  while  this  evening,  and  I  hope 
to  be  able  to  show  you  that  in  the  subject  we  are  to  consider 
we  are  really  dealing  with  one  of  the  most  important  factors 
in  the  evolution  of  our  earth-moon  system. 

All  intelligent  people  who  have  lived  by  the  seashore  are 
familiar  with  the  rise  and  fall  of  the  sea  which  takes  place 
twice  in  every  diurnal  rotation  of  the  earth  on  its  axis.  Long 
ages  ago  these  tides  ceased  to  be  a  mystery  to  man,  and  in 
fact  before  their  theoretical  explanation  was  mathematically 
explained  man  was  perfectly  acquainted  with  their  action, 
their  intensity,  their  maxima  and  minima,  known  as  spring 
and  neap,  and  most  important  of  all,  with  the  wonder- 
ful fact  that  in  some  mysterious  way  these  tides  were  con- 
nected with  the  position  of  the  moon  in  relation  to  the  sun. 
Both  Pliney  and  Aristotle  refer  to  the  alliance  between  the 
times  of  high  water  and  the  stage  of  the  moon. 

Not  however,  until  Sir  Isaac  Newton  in  1687  presented 
to  the  Royal  Society  his  immortal  Principia,  was  it  possible 
for  men  to  understand  the  abstract  principle  of  the  cause  of 
the  tides.  In  this  celebrated  work  Newton,  in  a  manner  which 
makes  it  seem  as  if  he  was  divinely  inspired,  unfolded  to  the 
astonished  world,  the  mechanical  theory  of  nniversal,  grav- 
itation, showing  that  every  particle  of  matter  in  the  universe 
attracts  every  other  particle  with  a  force  which  is  ever  pro- 
portionate to  the  co-attracting  masses,  and  inversely  propor- 
tionate to  the  square  of  the  distances  separating  them. 

The  moon,  therefore,  attracts  every  particle  of  matter  on 
our  earth,  both  solid  and  liquid.  The  solids,  however,  are 
not  enabled  to  yield  in  such  a  marked  way  as  the  liquids  are; 
for  the  latter  are  forced  by  the  moon's  attraction  to  rise  bodily 
toward  her  to  a  certain  extent,  and  in  this  way  cause  the 
phenomenon  of  high  tide.  It  must  not  be  forgotten  that  the 


TIDAL  EVOLUTION.  7 

solid  crust  is  also  to  a  certain  degree  attracted  to  the  moon, 
away  from  the  waters  on  the  distant  side  from  the  satellite,  thus 
leaving  the  waters  in  a  high  wave  behind.  This  is  the  explana- 
tion of  the  neap  tides.  The  intervening  positions  between  the 
two  high  tides,  that  is,  the  positions  which  are  as  it  were,  in 
quadrature  with  the  moon,  form  the  ebbs. 

Thus,  with  a  little  reflection,  we  find  that  the  earth  is 
forced  through  the  attraction  of  the  moon  to  depart  from  the 
spherical  form  and  made  as  it  were  to  bulge  out  into  an  oblate 
ellipsoid,  the  major  axis  of  which  keeps  forever  following  the 
direction  of  the  moon  in  her  ceaseless  journey  around  her 
primary. 

But  some  of  you  may  think  that  these  tides  certainly  are  of 
a  rhythmic  character.  Do  they  not  rise  and  fall?  Are  they  not 
a  very  pulsation  of  the  ocean,  now  strong,  now  weak,  but 
ever  changing  in  a  regular  periodic  succession  ?  And  have  I 
not  myself  just  given  the  rise  and  fall  of  the  tides  as  an  illus- 
tration of  rhythmic  phenomena? 

In  answer  to  this  I  will  simply  propose  that  we 
change  our  point  of  view.  No  doubt,  from  a  terres- 
trial and  therefore  limited  standpoint  the  tides  do  appear 
to  be  of  a  rythmic  character.  But  let  us  rise  from  the 
terrestrial  to  the  general,  to  the  truly  philosophical  point 
of  view,  rising  high  enough  to  view  the  whole  globe  at 
a  glance;  or  let  us,  perhaps,  rather  view  the  axial  rotation  of 
our  earth  from  the  standpoint  of  the  moon.  What  now  has 
become  of  the  rise  and  fall  of  the  tides  and  their  rythmic  char- 
acteristics? Where  now  will  we  detect  their  periodic  spring  and 
neap,  their  flood  and  ebb?  All  have  disappeared,  being  only 
relative  phenomena,  caused  by  our  terrestrial  surroundings  and 
confined  limited  point  of  view.  In  their  place  we  behold  only 
one  single  gigantic  tidal  wave,  extending  from  pole  to  pole 
parallel  to  the  earth's  axis,  forever  following  in  the  wake  of 
the  moon's  course. 

What  a  worthy  subject  it  would  be  for  us  this  evening  to 
consider  some  of  the  extraordinary  physical  phenomena  con- 
nected so  closely  with  the  action  of  the  tides,  such  as  their 
surprising  smallness  in  midocean,  in  the  Mediterranean  sea, 


8  TIDAL  EVOLUTION. 

the  Caspian,  the  Baltic  aad  other  confined  areas;  their  enor- 
mous heights,  on  the  other  hand,  in  such  places  as  the  English 
channel  and  the  Bay  of  Fundy.  The  high  tides  of  both  of  the 
latter  places  are  especiallyinteresting  to  me,  having  witnessed 
them  personally  from  the  end  of  the  three-mile  pier  at  Havre 
on  the  Channel,  and  from  the  wharfs  at  St.  John,  N.  B.,  on 
the  Bay  of  Fundy.  Time,  however,  will  not  permit  of  this, 
and  I  pass  on  at  once  to  the  consideration  of  the  dynamical 
question  of  the  friction  which  the  tides  are  causing  on  the 
earth  and  its  effect  upon  the  diurnal  motion  of  the  planet. 

No  truth  rests  on  more  firm  foundation  than  the  axiom 
that  work  cannot  be  accomplished  without  the  consumption 
ot  energy  in  some  of  its  forms.  This  is  based  upon  the  immu- 
table law  of  correlation  of  forces. 

Now  the  tides  are  performing  a  wronderful  amount  of  work, 
rebuilding  our  continents,  hollowing  out  bays  and  aiding  in 
the  formation  of  bars,  besides  raising  bodily  at  the  present 
time,  all  the  waters  of  the  earth  on  an  average  three  feet  every 
24  hours.  In  past  ages  the  force  displayed  was  much  greater, 
depending  of  course  upon  the  proximity  of  the  moon.  Thus, 
as  we  shall  see  a  little  later,  when  the  moon  was  only  40,000, 
instead  of  as  at  present  240,000,  miles  from  the  earth,  the 
tides,  in  place  of  averaging  three  feet,  did  indeed  average  648 
feet  in  height.  Such  tides  as  these  would  sweep  almost  every 
city  from  the  face  of  the  earth.  Just  reflect  upon  what  an 
enormous  amount  of  wrork  tides  like  these  must  have  been  able  to 
accomplish,  and  what  important  factors  they  must  have  been 
in  the  evolution  of  the  early  stages  of  the  earths'  crust. 

But  from  what  source  is  the  energy  derived  at  the  expense 
of  which  all  this  work  was  and  is  today  performed? 

As  the  moon  is  the  direct  cause  of  the  tides,  it  would,  at 
a  superficial  glance  appear  that  we  might  be  justified  in  at- 
tributing the  source  of  energy  to  our  satellite.  But  is  this 
true?  Will  it  hold  good?  No  doubt  it  seems  plausable,  but 
it  is,  nevertheless,  a  fallacy.  To  illustrate  this,  permit  me  to 
quote  an  illustration  from  Sir  Robert  Ball.  He  says  that  it 
is  one  of  those  cases  by  no  means  infrequent  in  dynamics, 
where  the  truth  is  widely  different  from  what  seems  to  be  the 


TIDAL  EVOLUTION.  9 

case,  and  illustrates  it  with  the  example  of  a  rifle  which  is  fired 
by  the  pulling  of  a  trigger  by  the  rifleman's  finger.  No  one 
would  assert  that  the  energy  by  which  the  rifle  ball  was  fired 
off  was  supplied  by  the  rifleman.  Certainly  not.  The  energy 
was  of  course  due  to  the  gunpowder,  and  all  the  rifleman  did 
was  to  provide  the  means  by  which  the  energy  stored  up  in 
the  gunpowder  became  liberated. 

In  almost  the  same  way  the  tides  raised  by  the  moon  are 
simply  the  originating  cause  whereby  a  certain  amount  of 
energy  stored  up  in  the  earth  itself  is  liberated  and  applied 
to  perform  such  work  as  the  tides  are  competent  to  perform. 

The  store  house  of  energy  upon  which  the  tides  through 
the  agency  of  the  moon  are  making  such  large  and  continuous 
drafts  is  to  be  found  in  the  momentum  stored  up  in  the  axial 
revolution  of  the  planet.  No  doubt  this  is  an  enormous  store 
house  of  energy.  No  doubt  it  seems  to  us  all  but  inexhausti- 
ble. But  as  the  power  drawn  from  it  by  the  tides  is  not 
replaced,  the  irresistible  consequence  is  that  the  momentum 
of  rotation  is  being  dissipated,  and  that  this  rotation  is  slowly 
but  surely  decreasing.  As  a  result  the  day  which  is  now  24 
hours  is  becoming  longer. 

If  I  am  not  mistaken,  it  was  Immanuel  Kant,  who,  more 
than  a  century  ago  first  called  attention  to  the  fact  that  the 
tides  in  rolling  from  east  to  west  were  reducing  the  earth's 
diurnal  motion.  He  showed  that  countless  aeons  of  time  may 
elapse  before  the  momentum  can  be  completely  exhausted, 
but  it  is  nevertheless  true  that  the  energy  is  decreasing  and 
the  relation  of  the  earth-moon  system  tending  toward  equilli- 
brium.  At  present  the  axial  revolution  of  the  earth  is  not 
measurably  longer  than  it  was  100  years  ago.  Even  in  1000 
years  the  change  in  the  length  of  the  day  may  perhaps  be 
only  a  fraction  of  a  second.  But  the  importance  attached  to 
this  dissipation  of  momentum  lies  in  the  fact  that  this  phe- 
nomenon, though  acting  majestically  slow,  is  not  of  a  rythmic 
nature  but  continues  right  on  ceaselessly  and  eternally  in  the 
same  direction. 

L,a  Place's  celebrated  theory  that  opposite  currents  are  as 
to  their  effect  upon  the  rotation  of  the  earth  as  plus  and  minus 


w  TIDAL  EVOLUTION. 

naught,  and  that  there  are  no  forces  at  work  in  nature  which 
do  not  always  find  their  compensating  opposites,  I  believe 
does  not  hold  good  in  the  case  of  tidal  friction.  Silently  and 
slowly  though  it  be,  the  tides  are  nevertheless  uninterruptedly 
acting  as  a  brake  upon  the  rotation  of  the  earth,  and  in  mil- 
lions of  years  the  accumulated  effect  will  not  only  become 
appreciable  but  even  of  a  startling  magnitude.  Many  attempts 
have  been  made  to  compute  this  increase  in  the  length  of  the 
day,  but  of  course  the  results  must  be  taken  with  a  good  deal 
of  reserve.  Dr.  J.  B.  Mayer,  after  an  elaborate  analysis  of 
the  subject,  arrives  at  a  value  of  1-16  of  a  second  for  every 
2500  years. 

Perhaps  the  best  authority  on  the  matter  is  Sir  William 
Thomson,  who  in  a  careful  calculation  of  the  age  of  the 
earth's  crust  shows  that  it  cannot  be  less  than  10,000,000 
years,  because  the  figure  of  our  globe  differs  so  little  from 
equilibrium  in  planetoid  compression — that  is,  the  polar  com- 
pression is  nearly  the  same  as  that  which  the  present  diurnal 
motion  would  produce  in  a  molten  world.  Nearly  the  same, 
but  not  quite.  What  may  be  the  value  of  this  trifling  dif- 
ference? The  product  of  this  discrepancy  will  furnish  us  with 
an  approximation  of  the  relative  amount  of  the  lengthening 
of  the  day.  The  same  high  authority  has  arrived  at  a  valua- 
tion of  i  per  cent  for  20,000,000  years.  Out  of  curiosity  I 
have  myself  calculated  what  this  i  per  cent  means  in  fractions 
of  diurnal  motion,  and  have  found  it  to  roughly  correspond  to 
864  seconds,  or  14^2  minutes.  Therefore,  if  any  assurance 
can  be  placed  on  the  figures  which  Sir  William  Thomson  sub- 
mits, it  would  appear  that  the  earth  today  does  require  14^ 
minutes  more  to  perform  one  revolution  on  its  axis  than  it  did 
20,000,000  years  ago.  It  only  needs  to  be  added  that  this  is 
not  presented  as  an  accurate  result,  but  rather  as  an  inter- 
esting speculation. 

But  in  accordance  with  Galileo's  third  law  of  motion, 
that  to  every  action  there  must  always  be  an  equal  and  oppo- 
site reaction,  it  may  be  asked  in  what  way  this  reaction 
exhibits  itself  in  the  tidal  action  of  the  earth-moon  system. 
The  moon,  as  we  have  seen,  acts  upon  the  earth  by  retarding 


TIDAL  EVOLUTION.  n 

her  axial  rotation;  the  earth  conversely  reacts  upon  the  moon 
by  pushing  her  further  and  further  away.  In  this  manner  the 
reaction  exhibits  itself.  At  first  thought  there  does  not  seem 
to  be  much  importance  attached  to  this  phenomenon,  but  a  little 
reasoning  will  soon  show  that  in  this  reaction  we  are 
dealing  with  a  problem  which  for  far-reaching  conclusions  is 
perhaps  unparalled  in  the  whole  solar  system. 

At  present  the  distance  separating  the  two  bodies  is  about 
240,000  miles,  and  the  length  of  the  day  is  about  24  hours. 
If  the  theory  of  tidal  friction  be  true,  then  both  the  distance 
of  the  moon  and  the  position  of  the  earth  must  have  been 
shorter  yesterday  than  today,  shorter  the  day  before  yesterday 
than  yesterday,  and  so  on.  Looking  backward  a  million  years, 
the  revolution  was  perhaps  only  some  minutes  shorter  than  it 
is  today,  and  the  radius  of  the  moon 's  orbit — which  of  course 
is  the  distance  of  the  satellite  from  the  earth — was  correspond- 
ingly shorter. 

Before  arriving  at  the  critical  result  of  this  analysis,  there 
are  two  other  dynamical  elements  which  must  be  taken  into 
consideration  and  thoroughly  understood.  First,  that  in 
accordance  with  Keppler's  second  law,  that  the  radius  vector 
always  describes  equal  areas  in  equal  times,  it  follows  that  the 
moon  in  past  ages  must  have  completed  her  lunation  in  shorter 
periodic  time  than  at  present.  Second,  that  the  quicker  the 
earth  turns  on  her  axis  the  more  centrifugal  force  becomes  dis- 
played and  that  if  the  rotation  becomes  too  quick  the  centrif- 
ugal force  will  become  so  pronounced  that  it  will  overcome 
the  cohesion  of  the  particles  of  the  earth  and  the  gravitation 
which  attracts  them  toward  the  center.  The  result  wTould  be 
that  the  globe  would  fly  to  pieces,  or,  which  is  still  more 
likely,  would  leave  a  ring  behind  from  off  its  outward  bulged 
equatorial  zone. 

Thus  then  by  retracing  our  steps  backward  in  time  in 
accordance  with  tidal  evolution  we  arrive  at  a  critical 
time,  when  the  moon  must  have  been  grazing  the  surface  of 
the  earth,  and  when  one  revolution  of  the  earth  on  its  axis 
must  have  corresponded  to  one  lunation  of  the  moon.  It 
would  appear  that  the  time  required  was  about  three  hours. 


12  TIDAL   EVOLUTION. 

Prof.  G.  H.  Darwin  of  Oxford  has  calculated  that  this 
state  of  affairs  of  the  earth-moon  system  could  not  have 
existed  less  than  50,000,000  years  ago. 

Studying  the  theory  of  tidal  evolution  of  the  past,  we 
therefore  find  that  it  insensibly  leads  us  to  a  belief  that  the 
moon  was  once  a  part  of  this  earth,  and  that  from  a  prepon- 
derance of  the  centrifugal  force  it  became  in  some  way  or 
other  fractured  off  and  left  behind*  This,  of  course,  must 
have  taken  place  when  the  matter  of  the  system  was  still  in  a 
plastic  or  molten,  or  perhaps  even  in  a  gaseous  state. 

But  plainly  this  is  onlyan  illustration  of  L,a  Place's  cel- 
ebrated nebular  hypothesis — that  all  the  ponderable  material 
now  constituting  the  various  bodies  of  the  solar  system  once 
have  existed  as  a  rarefied  mass  of  gaseous  matter — a  nebula — 
and  that  as  this  nebula  cooled  by  radiating  its  heat  into  space,  it 
contracted  and  was  gradually  shaped  into  its  present  form. 

In  the  future  the  moon  will  continue  to  retard  the  earth 
in  her  diurnal  motion  and  to  increase  and  separate  herselt 
more  and  more  from  her  primary.  In  the  same  way  that  the 
earth  has  caused  our  satellite  to  complete  one  revolution  on 
her  axis  in  the  same  time  as  is  required  for  her  lunation 
(thereby  forcing  her  to  always  exhibit  the  same  face  toward 
the  earth) ,  in  exactly  the  same  way  the  moon  will  compel  our 
earth  to  slow  down  the  time  of  the  diurnal  motion  until  it 
corresponds  exactly  to  the  moon's  periodic  time.  It  has  been 
computed  that  the  length  of  the  month  as  well  as  the  length 
of  the  day  at  that  important  epoch  will  be  about  54  of  our 
days  or  about  1400  hours. 

We  will  then  have  what  is  known  as  a  stable  dynamical 
equilibrium,  with  the  earth  and  the  moon  always  presenting 
the  same  faces  toward  each  other,  and  this  state  of  affairs 
would  last  forever,  providing  that  no  extraneous  forces  were 
brought  to  bear  on  the  system. 

But  as  every  particle  of  matter  attracts  every  other  par- 
ticle in  the  universe,  it  follows  that  the  sun  also,  must, 
in  the  same  way  as  the  moon,  raise  tides  on  the  earth.  So 
the  sun  does,  too,  but  as  the  tide  generating  power  of  attraction, 
as  far  as  distance  goes,  acts  on  the  inverse  square,  we  have  so 


TJDAL   EVOLUTION.  13 

far  not  found  it  necessary  to  even  mention  the  solar  tides. 
But  when  the  earth-moon  system  has  attained  equilibrium  the 
sun-raised  tides  will  continue  right  on  in  their  action.  To  be 
sure,  they  are  very  small  compared  to  those  raised  by  the 
moon,  but  it  is  well  to  remember  that  it  is  just  these  small 
forces  acting  day  in  and  day  out,  silently,  quietly,  persistently, 
uninterruptedly  in  the  same  direction,  which  in  the  end 
accomplish  stupendous  results.  When  the  earth  and  moon 
shall  have  come  to  a  mutual  rest,  the  solar  tides  will  continue 
to  retard  the  earth  in  her  diurnal  motion  until  at  last  the  day 
will  become  longer  than  the  month. 

This  may  seem  to  many  to  be  an  impossible  state  of  af- 
fairs— that  the  month  which  is  now  27  times  longer  than  the 
day  should  actually  become  shorter.  But  why  not?  If  these 
conditions  existed  today  they  would  be  just  as  natural  to  us  as 
our  present.  In  fact,  we  are  able  with  a  great  deal  of  satis- 
faction to  corroborate  our  reasoning  with  a  remarkable  example 
in  our  solar  system.  The  planet  Mars  is  but  little  more  than 
half  the  size  of  our  earth.  We  are  therefore  justified  in 
believing  that  this  brother  sphere  has  passed  through  his 
evolution  quicker  and  is  further  along  the  road  of  his  destiny 
than  is  the  case  with  our  earth.  With  this  in  mind  it  is 
interesting  to  find  that  in  the  case  of  this  planet  and  his  satel- 
lite Phobes,  the  Martian  day  is  actually  three  times  longer 
than  the  periodic  time  of  the  satellite — a  signal  prophesy  ot 
the  future  of  our  own  earth-moon  system. 

For  the  same  reason  that  we  expected  Mars  to  be  in 
advance  of  our  earth  in  his  evolution,  we  would  anticipate 
Jupiter  on  the  other  hand  to  befar  behind.  On  this  giant  planet, 
which  is  so  much  larger  and  so  much  farther  distant  from  our  sun 
— its  center  of  heat  and  attraction,  we  may  confidently  expect 
to  find  conditions  prevailing  which  existed  on  our  earth  many 
millions  of  years  ago.  And,  indeed,  in  this  we  shall  not 
find  ourselves  to  have  judged  wrong.  It  does  not  take  very 
many  observations  with  a  powerful  telescope  to  tell  that  this 
planet  is  not  solid,  but  is  rather  in  a  plastic,  if  not  even  in,,  a 
molten  condition.  But  most  significant  of  all,  his  axial  revo- 
lution is  accomplished  in  about  10  hours — a  phenomenon  which 


447O65 


14  TIDAL  EVOLUTION. 

indeed  corresponds  to  the  letter  with  what  tidal  evolution  tells 
us  was  the  past  conditions  of  our  own  earth. 

Then  again  observe  the  comprehensive  fact  that  both 
Mercury  and  Venus,  the  two  planets  nearest  to  the  sun, 
always,  according  to  the  most  reliable  observations,  turn  the 
same  face  toward  the  sun.  Tidal  friction  has,  as  it  were, 
arrested  the  axial  revolutions  of  both  of  these  planets,  and 
forced  them  to  forever  pay  obeisance  to  their  primary. 

Leaving  the  so'ar  system  and  passing  outward  to  the 
siderial  we  soon  find  further  corroboration  of  our  theory. 
We  have  seen  this  evening  that  one  of  the  effects  of  tidal 
friction  is  that  the  two  attracting  bodies  keep  pushing  further 
and  further  away  from  each  other.  In  the  case  of  the  earth- 
moon  system  the  pushing  is  pretty  well  one-sided  on  account 
of  the  great  difference  in  size  of  the  two  bodies.  But  suppose 
that  both  bodies  were  of  about  the  same  mass.  What  would 
be  the  result?  This  is  what  the  consequence  would  be.  The 
earth  would,  push  the  moon  and  the  moon  the  earth  about  an 
equal  amount,  and  this  would  in  its  turn  give  rise  to  exceed- 
ingly elongated  elliptical  orbits.  Now  one  of  the  most 
remarkable  facts  connected  with  nearly  all  the  binary  systems 
of  double  stars  far  away  in  the  bosom  of  unmeasurable  space 
is  their  exceedingly  eccentric  elliptical  orbits,  caused  undoubt- 
edly by  mutual  tidal  action  of  the  components  of  the  systems. 
My  authority  for  this  statement  is  Herr  T.  J.  J.  Lee  of  Berlin. 

There  is  another  collateral  consequence  which  must  follow 
from  a  combination  of  tidal  action  and  gravitation  on  a  primi- 
tive plastic  planet.  During  the  course  of  evolution  the  earth's 
mass  must  have  suffered  a  screwing  motion  so  that  the  polar 
regions  have  traveled  a  little  from  west  to  east,  relative  to  the 
equator.  Prof.  G.  A.  Darwin  of  Oxford  thinks  that  this  fur- 
nishes a  possible  explanation  of  the  north  and  south  trend  of 
our  great  continents. 

Tidal  evolution  has  indeed  furnished  explanations  for 
many  important  questions  about  the  remote  past  and  dim, 
distant  future  of  the  bodies  of  our  solar  system.  It  has  per- 
haps helped  us  along  one  more  step  in  our  painstaking  search 
for  truth  and  groping  for  exact  knowledge.  This  is,  however, 


TIDAL  EVOLUTION.  15 

all  that  it  has  done.  The  mystery  of  the  great  whole  and  the 
origin  of  the  universe  it  leaves  as  great  as  ever.  Sometimes 
we  feel  hopeful  that  eventually  the  genius  of  man  will  unfold 
it  all.  And  indeed  we  have  good  cause  and  a  perfect  right  to 
be  proud  of  what  the  human  intellect  has  been  able  to  accom- 
plish. But  it  seems  to  me  that  every  step  ahead  only  tends 
to  show  the  greater  extent  of  the  unknowable.  As  Carlyle 
has  so  finely  said  in  his  Sartor  Resartus:  *' System  of  Nature! 
To  the  wisest  man,  wide  as  is  his  vision,  nature  remains  of 
quite  infinite  depth,  of  quite  infinite  expansion;  and  all  exper- 
ience thereof  limits  itself  to  some  few  computed  centuries  and 
measured  square  miles.  The  course  of  nature's  phases  on  this, 
our  little  fraction  of  a  planet,  is  partially  known  to  us;  but 
who  knows  what  deeper  courses  these  depend  on;  what 
infinitely  larger  cycles  of  courses  our  little  epicycle  revolves 
upon.  To  the  little  tadpole  or  minnow  every  cranny  and 
pebble,  and  quality  and  accident  of  its  little  native  creek  may 
have  become  familiar,  but  does  the  minnow  understand  the 
ocean  tides  and  periodic  currents,  the  trade  winds  or  mon- 
soons or  the  moon's  eclipses,  by  all  of  which  the  conditions  of 
its  little  creek  is  regulated,  and  may  (immiraculously  enough) 
be  quite  overset  and  reversed  ?  Just  such  a  little  minnow  is 
man,  his  creek,  this  planet;  his  ocean,  the  immeasurable  all; 
his  monsoons  and  periodic  currents,  the  mysterious  course  of 
nature  through  aeons  and  aeons." 


University  of  California 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 

405  Hilgard  Avenue,  Los  Angeles,  CA  90024-1388 

Return  this  material  to  the  library 

from  which  it  was  borrowed. 


REC'DYRLAPR  1 


ttt 


TTNTVERSTTY  of  CALIFORNIA 

AT 

3  ANGELES 
IJBR 


r: 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


000  779  340     9 


PLEAfifc  DO   NOT    R£M£ 
THIS   BOOK  CARDS 


University  Research  Library 


Univeri 
Sout 
Lib 


